The present application is based on Japanese priority applications No.2001-324433 filed on Oct. 23, 2001 and No. 2001-355228 filed on Nov. 20, 2001, the entire contents of which are hereby incorporated by reference.
The present invention generally relates to electronic materials and more particularly to a microwave dielectric composition and an integrated ceramic module that uses such a microwave dielectric composition.
In the technology of mobile telecommunication such as cellular phones or in the technology of wireless information technology such as wireless LANs, there exists a stringent demand of compact size and lightweight construction for the terminal devices used therein in addition to the demand for transmitting large amount of information.
In order to achieve such reduction of size and weight of terminal devices, investigations are being made on the technology of high-density mounting and further on an integrated module in which a high-frequency circuit is integrated.
The size and performance of passive components such as antenna or filter depend heavily on the material used for the component. It should be noted that the wavelength of a radio wave is compressed, in a dielectric material having a dielectric constant xcex5, to 1/xcex5 the wavelength of the radio wave in a free space. Thus, the line length in a circuit, and hence the size of the component, can be reduced with increasing dielectric constant of the dielectric material used therein. Thus, increase of the dielectric constant of the material constituting the passive component is an important factor for miniaturizing the components.
On the other hand, there exists a different demand, in certain passive components such as filters and resonators in which occurrence of insertion loss is inevitable, that the dielectric material has a high Q value for minimizing the insertion loss.
Further, it is desirable to use a material of low electric resistance such as Ag, Cu or Au in passive components such as a filter circuit formed of inductance and capacitance, for reducing loss caused by the conductive lines in the passive component. However, all of these low-resistance metals have a relatively low melting point of about 1000xc2x0 C. (for example, Ag has a melting point of 960xc2x0 C., Cu has a melting point of 1083xc2x0 C., Au has a melting point of 1063xc2x0 C.), and thus, there is a need of suppressing the firing temperature of the ceramics constituting the dielectric material in the passive elements to the temperature not exceeding the melting point of the foregoing metal elements in order that such low-resistance metal material is introduced into the passive components.
Thus, in order to realize a compact, lightweight and high-performance passive elements, there is a need of a microwave dielectric composition having a large dielectric constant and high Q value, and simultaneously capable of being fired at low temperatures.
In the transmission line used in electronic circuits, and the like, such as a microwave strip line, on the other hand, there is a demand of a microwave dielectric composition having as small dielectric constant as possible for realizing high signal transmission rate. In this case, too, there is a demand that the microwave dielectric composition has a high Q value for minimizing the transmission loss. Further, there is a demand that the microwave dielectric composition is capable of being formed at low firing temperature in view of the need of forming a laminated structure together with a metal interconnection layer.
However, conventional microwave dielectric composition, while having the desired high or low dielectric constant and high Q value, has to be fired at a high temperature exceeding 1500xc2x0 C., and it has not been possible to construct a passive component or transmission line having a structure laminated with a metal wiring layer.
Thus, in conventional passive components or transmission lines, a ceramic material capable of being fired at low temperatures has been used for the microwave dielectric composition. However, such ceramic materials capable of being fired at low temperatures have a Q value of about 200 at the best, and it has been difficult to realize a Q value exceeding 1000.
Meanwhile, it is desirable that the ceramic components such as antenna, filter, capacitor, and the like form a unitary, integrated ceramic module together with a ceramic signal transmission line connecting the foregoing components electrically from the viewpoint of reducing the size and weight of the terminal devices. However, the microwave dielectric composition used for antenna, filter or capacitor is required to have a large dielectric constant in addition to the high Q value as noted before, while the microwave dielectric composition used for the signal transmission line is required to have a low dielectric constant in addition the high Q value.
When attempt is made to form an integral module by laminating the components formed of ceramic materials of different nature, it is inevitable to conduct a process of firing the laminated structure in which different ceramic material layers are laminated in the same ambient at the same temperature. However, because of the different firing shrinkage characteristics of the ceramic materials, there is a tendency that problems such as poor adherence between the ceramic layers, formation of cracks or delamination, may take place in such a firing process as a result of the different firing shrinkage characteristics of the ceramic materials and the firing shrinkage caused at the time of the firing process.
Accordingly, it is a general object of the present invention to provide a novel and useful microwave dielectric composition wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a microwave dielectric composition having a high Q value and high dielectric constant or high Q value and low dielectric constant and is capable of being fired at a low temperature of 900xc2x0 C. or less.
Another object of the present invention is to provide an integrated ceramic module formed of a multi-functional and multilayer laminated structure, in which a ceramic dielectric layer having a high Q value and high dielectric constant and formed with an electronic component therein and a ceramic dielectric layer having a high Q value and a low dielectric constant and formed with a transmission line therein are laminated.
Another object of the present invention is to provide a high-dielectric microwave dielectric composition, characterized by oxide ceramic particles, and an oxide-base amorphous glass, in which the oxide ceramic particles are dispersed, or an oxide-base crystallized glass, wherein the oxide ceramic particles contains at least one component selected from the group consisting of BaTi4O9, Ba2Ta9O20, Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3, Ba(Mg1/3Ta2/3)O3, Ba(CO1/3Ta2/3)O3, Ba(CO1/3Nb2/3)O3, Ba(Ni1/3Ta2/3)O3 and TiO2.
According to the present invention, it becomes possible to obtain a high-dielectric or low-dielectric microwave dielectric composition having a very high Q value and still capable of being fired at a low temperature of about 900xc2x0 C. or less, by using the ceramic particles selected from the foregoing group of BaTi4O9, Ba2Ta9O20, Ba (Zn1/3Ta2/3)O3, Ba (Zn1/3Nb2/3)O3, Ba(Mg1/3Ta2/3)O3, Ba(Co1/3Ta2/3)O3, Ba(Co1/3Nb2/3)O3, Ba(Ni1/3Ta2/3)O3 and TiO2 and having a high Q value and an oxide-base amorphous glass or oxide-base crystallized glass having a high Q value.
Another object of the present invention is to provide an integrated ceramic module characterized by a first ceramic dielectric layer containing a glass as a sintering agent and having a high dielectric constant and a high Q value, the first ceramic layer being formed with an electronic component, and a second ceramic dielectric layer laminated on the first ceramic dielectric layer, the second ceramic dielectric layer containing a glass as a sintering agent and having a low dielectric constant and a high Q value, the second ceramic dielectric layer being formed with a signal transmission line.
According to the present invention, glasses are added to the first and second ceramic dielectric layers as respective sintering agents, and because of this, it becomes possible to adjust the sintering characteristics at the time of firing these ceramic layers from respective green sheets to be coincident between the first ceramic layer and the second ceramic layer. As a result, it becomes possible to fire the first ceramic dielectric layer and the second ceramic dielectric layer simultaneously in the state that the respective green sheets are laminated with each other.